1. Field of the Invention
The present invention relates to a solid-state imaging device and an electronic device including the solid-state imaging device.
2. Description of the Related Art
Solid-state imaging devices are widely used as image input devices for various types of electronic devices such as digital still cameras, digital single-lens reflex cameras, digital video cameras, and portable terminals.
A solid-state imaging device includes a number of pixels (picture cells) arranged in a two-dimensional matrix such as an array. The pixel has at least a photodiode as a photodetecting portion to convert light into electrons and a transfer portion. The transfer portion in a CCD (charge-coupled device) solid-state imaging device has a vertical transfer portion and a horizontal transfer portion formed by CCD elements, for example. The transfer portion in a CMOS (Complementary Metal-Oxide-Semiconductor) solid-state imaging device (CMOS image sensor) has an amplifier circuit portion to convert electrons from the photodiode into voltage and amplify and transfer the voltage, for example.
A number of pixels are adjacent to each other in the solid-state imaging device. Therefore, part of light incident on a photodiode of a pixel may be mixed in an adjacent pixel (crosstalk).
Crosstalk occurs due to modulation (such as reflection, diffraction, or scattering) of part of incident light. Such occurrence of crosstalk between pixels affects an output, that is, resulting image data. Specifically, bright spots may be generated in an image that should be black, for example, so that image data intended may not be accurately obtained.
Such occurrence of crosstalk will be described referring to, as an example, a case where the aforementioned modulation is reflection.
FIG. 1 shows a pixel configuration of a solid-state imaging device of the related art.
In a solid-state imaging device 101 of the related art, part of light (L1′ in the figure) incident on a photodiode 117 of a pixel 101a (cell size x′) is reflected by a surface of a semiconductor substrate including the photodiode 117 and is leaked to an adjacent pixel. Therefore, it is difficult to prevent crosstalk from occurring between pixels in every solid-state imaging device having a photodiode, including any of CCD/CMOS solid-state imaging devices.
There has been proposed a method of providing an antireflective film on a substrate surface as a measure for the problem. However, this method is known to have other problems such as a change in spectral characteristics.
Further, incident light may be reflected by a member around the photodiode before reaching the photodiode (L2′ in the figure). For example, the solid-state imaging device 101 has a peripheral wiring portion 114 with a multilayer structure provided around the photodiode. Accordingly, incident light is repeatedly reflected by wiring layers of the peripheral wiring portion 114 (a first wiring layer 111, a second wiring layer 112, and a third wiring layer 113 shown in FIG. 1) and is leaked to and mixed in an adjacent pixel in a route different from that of the light (L1′) reflected by the substrate surface.
As a method of preventing such crosstalk due to repeated reflection, there has been proposed a method of separately providing a light-shielding wall between pixels. However, this method is complicated because it may be necessary to carry out a separate process of forming the wall. Further, if such a wall is provided, pixel area increases, thereby preventing a reduction in size of the device (refer to Japanese Unexamined Patent Application Publication No. 2005-277404).